As a gas control system adapted to transport material gas used for deposition treatment in a semiconductor manufacturing process, as disclosed in Patent Literature 1, there is a gas control system adapted to introduce carrier gas into a tank containing a material, lead out material gas produced by vaporization of the material together with the carrier gas from the tank as mixed gas, measure the concentration of the material gas included in the mixed gas, and perform PID control of the flow rate of the carrier gas so as to bring the measured concentration close to a predetermined target concentration.
However, in the conventional gas control system, the tank before operation is in a state of being filled with the material gas of high concentration produced by vaporization in advance, and therefore when the mixed gas including the high concentration material gas is led out of the tank at once just after the operation, the concentration of the material gas included in the mixed gas momentarily increases. Also, when bringing the measured concentration close to the target concentration using the PID control, an action to increase the flow rate of the carrier gas at once is performed at the start of the control because of the time delay in concentration change. These phenomena cause the problem of occurrence of overshoot greatly exceeding the target concentration. Further, the concentration of the material gas produced in the tank by the vaporization in advance is varied by multiple factors such as material factors including the nature, amount, and so on of the material, apparatus factors including the inside diameter of each pipe member, the capacity of the tank, and the like, and external factors including temperature and the like. This causes the problem that when the material gas whose concentration is varied by the multiple factors is led out of the tank at once in the initial stage where the carrier gas is introduced, a change in the concentration of the material gas does not exhibit reproducibility. Further, due to these problems, the total amount of the material gas to be led out of the tank is difficult to control using only the PID control used for the conventional gas control system.